1. Field of the Invention
Aspects of the present invention relate to a battery pack, and more particularly, to a battery pack that can prevent both deformation due to external impact and leakage of electrolyte.
2. Description of the Related Art
Secondary batteries are more economical than disposable batteries since they are rechargeable. Moreover, because secondary batteries are now being designed to be smaller but with higher capacity, secondary batteries are more widely used as power sources for handheld electronic/electrical appliances such as mobile phones, notebook computers, camcorders, digital cameras, etc. Types of secondary batteries include nickel-cadmium (Ni—Cd), nickel-metal hydride (Ni-MH), nickel-zinc (Ni—Zn), lithium (Li) ion, lithium metal and lithium polymer batteries.
Among these secondary batteries, lithium secondary batteries are widely used because they are compact, and have high capacity, high operating voltage and high energy density per unit weight. A lithium secondary battery may be classified into a can type or a pouch type according to the shape of the casing accommodating an electrode assembly. An electrode assembly includes a positive electrode plate, a negative electrode plate and a separator. Can type batteries may be further sub-classified into a cylindrical type and a prismatic type.
Lithium secondary batteries may be classified according to the kind of the electrolyte into a lithium metal battery or lithium ion battery, both of which use a liquid electrolyte, and a lithium ion polymer battery, which uses a solid electrolyte. Generally, a lithium ion battery using a liquid electrolyte employs a can type casing while a lithium ion polymer battery using a solid electrolyte employs a pouch type casing because the solid electrolyte is less likely to leak than the liquid electrolyte.
When a lithium secondary battery has a pouch type casing, an electrode assembly is accommodated in a lower member of the pouch type casing. Then, the lower member of the pouch type casing is covered by an upper member, and sealing parts initially formed at edges of the upper and lower members of the pouch type casing are joined and sealed. This assembly is called a bare-cell type secondary battery. The bare-cell type secondary battery is then electrically connected to a protection circuit board that includes a protection device to prevent damage to the battery because of any abnormal operations such as excess charging, excess discharging or excess current.
The secondary battery connected to the protection circuit board can be formed into a hard-pack battery pack that includes a separate outer case or an inner-pack type battery pack to make provision for tubing or labeling. In these situations, a front end portion of the bare cell from which positive and negative electrode tabs project is vulnerable to external impact. Accordingly, the pouch-type casing may be easily damaged by the external impact, which may result in a short circuit between the positive and negative electrode tabs as well as leakage of electrolyte from the damaged casing.
To solve these problems, in Korean Patent Publication No. 10-2005-0096288, a method is disclosed for adding a reinforcing plate to an outer case to prevent damage to a pouch type casing from external impact. However, the inventive method disclosed in Korean Patent Publication No. 10-2005-0096288 provides limited protection to the casing from external impact because there is a gap between the reinforcing plate and the sealing part of the pouch type casing. That is, since there is a gap between the bare cell and the protection circuit board, the protection circuit board or the bare cell may be moved by the external impact, and thus a short circuit between positive and negative electrode tabs may occur.